This invention relates to a weatherable film which is useful for forming a protective surfacing layer for a substrate. The present invention is especially applicable to the formation of a protective surface layer on flexible sheet materials, such as vinyl fabrics.
Vinyl outdoor fabrics are used in a wide range of applications such as in awnings, canopies, flexible signs, boat and pool covers, tarps and covers for trucks, and the like. Such fabrics are also widely used in constructing outdoor building structures, such as air inflated buildings and tension supported structures. In all of these outdoor applications, it is important that the vinyl fabric be able to withstand such environmental factors as extreme hot and cold temperatures, ultraviolet radiation and atmospheric pollution. The fabrics are usually produced in various colors and it is desirable that the fabric be resistant to mildew, fading by sunlight, soiling, and staining from airborne pollutants.
To maintain the appearance of the vinyl outdoor fabrics, many manufacturers recommend regular cleaning and the periodic application of a sealer composition, such as an acrylic polymer sealer. However, these procedures involve significant labor and material costs, and are therefore undesirable.
Neumann, et al. U.S. Pat. No. 4,556,589 discloses a protective fluoropolymer containing sealing layer for vinyl substrates which is applied as an aqueous dispersion to the vinyl substrate and thereafter heated and dried to provide weatherability and resistance to soiling and staining. However, coating processes such as that disclosed in the Neumann et al patent require special coating equipment which is often not available to producers of vinyl fabrics. Furthermore, such coating processes can result in uneven or incomplete coverage, pinholes or blisters, especially with fabrics having a textured surface.
Another approach which has been employed for protecting vinyl fabrics is to apply to the fabric a protective transparent film of a weatherable polymer, such as a fluoropolymer. One such commercially available film which has been widely used for this purpose is produced and sold by DuPont under the trademark Tedlar.RTM.. DuPont's Tedlar.RTM. film is an oriented polyvinyl fluoride film having excellent weatherability and stain resistance. However, the properties of this film which contribute to its excellent weatherability and stain resistance make it difficult to apply the film to a vinyl substrate. Application of the film requires a secondary process to make it adherent to the vinyl. Typically, this involves the application of solvent based adhesives. The volatile solvents required for application of the adhesive require special equipment to control the solvent vapors in the workplace environment. The natural non-adherent properties of the film also render it susceptible to delamination from the underlying vinyl substrate under severe conditions. A further significant drawback of the Tedlar.RTM. film in these applications is its inherent tendency to craze or stress whiten when folded. The vinyl fabrics are frequently creased or folded during handling or installation. The Tedlar.RTM. PVF film has a tendency to craze or stress whiten when folded, thus forming a permanent discoloration or crease line on the fabric.
It is an object of the present invention to overcome the disadvantages and limitations of the aforementioned prior art approaches to protecting vinyl fabrics.
It is a further object of the present invention to provide a film which can be applied as a protective weatherable surfacing layer for various substrates, and which does not require the use of volatile solvents or solvent based adhesives for its application.
More specifically, it is an object of the present invention to provide a protective film of the type described which can be applied to various types of substrates and which has a self-bonding capability so that it can be economically and easily applied to the substrate with the use of heat and pressure.
It is still another object of the present invention to provide a protective film of the type described which is not susceptible to crazing or stress whitening.
It is still another object of the invention to provide a film of the type described which, when applied to the substrate, forms a adherent bond which is not susceptible to delamination.
Still another object of the present invention is to provide a protective film of the type described which imparts to a substrate excellent soil and stain resistance properties.